Image acquisition method using optical transfer medium such as optical fibers are widely being used for medical instruments including medical endoscope, industrial devices for inspecting sewer pipes, an inner part of a collapsed building, an inner structure of a building, etc. For example, endoscope devices using optical fibers are disclosed in Korean laid-open patent publication Nos. 10-2005-0111011, Korean patent publication 10-0945280, etc.
In general, image acquisition techniques using optical fibers can be divided into a scanner-free method and a scanning method. Here, in case of the scanner-free method, since a single optical fiber cannot transfer image for the wide area, the scanner-free method uses an optical fiber bundle instead of a single optical fiber.
In case of scanner-free method, a number of bundled optical fibers are arranged at the input and the output in the same order such that the intensity of light which is transferred through one optical fiber at the input becomes one point at the output. A lens for imaging is attached to one end of the optical fiber bundle so that an image of object is formed at the end of the bundle and then each optical fiber constituting the bundle transfers image pixels to the outside. The advantage of the scanner-free method is that an image of object can be obtained for wide area in real time without need to analyze an image.
However, in the scanner-free method, since a number of optical fibers are needed to obtain high resolution, a diameter of the optical fiber bundle must be enlarged. Further, the optical fiber bundle having many of optical fibers is less flexible, and the number of bad pixels increases when the optical fiber is cut as time goes by. Further, if a thick bundle is inserted into a patient's body, the bundle is contact with a living body's tissue, thereby causing a severe friction. Therefore, the friction generates inconveniences such as pain and even a destruction of inner tissues.
Also, there is another problem that a pixelation of image occurs and thus, the quality of image is decreased. Referring to FIG. 1, FIG. 1(a) shows an image obtained with the optical fiber bundle and each of optical fiber constituting an optical fiber bundle forms one pixel in the image.
FIG. 1(b) shows an example of a target image which is a cell of a human body. As shown in FIGS. 1(a) and (b), if the size of a sample, e.g., cell, in the target image is less than the diameter of the optical fiber constituting an optical fiber bundle, an image is pixelated and the sample is hardly discerned as shown in FIG. 1(c). The resolution of the image is determined by the number of optical fibers constituting the optical fiber bundle and thus, the resolution of the image is low as can be seen in FIG. 1(c).
As an alternative to the scanner-free method, a scanning method is provided. In the scanning method, a condensing lens and a scanner are attached to the end of a single optical fiber and an object to be measured is scanned in a scanning method. In the scanner-free method, light is focused on one point at a time and a reflected light is obtained through an optical fiber. Therefore, to obtain an image over a wide area, a scanner must be installed to scan focused light.
As such, in the scanner-free method, it is advantageous that the diameter can be very small since a single optical fiber is used. However, since a lens and a scanner must be installed at the end of the fiber, the reduction of diameter is not substantial. Further, a further element such as a scanner must be installed and the image acquisition rate is low due to the scanning speed of the scanner. Moreover, the image quality is decreased by malfunction of the scanner.